Electrical resistor which can be adjusted as to resistance value



Oct. 1, 1968 G. w. WOOD 3,404,361

ELECTRICAL RESISTOR WHICH CAN BE ADJUSTED AS TO RESISTANCE VALVE Filed Sept. 28, 1966 F/GI/ M Z l2 Z4 54 50 54 INVENTOR GEORGE W W000 ATTORNEY United States Patent 3,404,361 ELECTRICAL RESISTOR WHICH CAN BE 'ADJUSTED AS TO RESISTANCE VALUE 1 George, W. Wood, Hammonton, N.J., assignor to IRC, Inc., Philadelphia, Pa.

Filed Sept. 28, 19 66, Ser. No. 582,578 7 Claims, (Cl. 338-143) ABSTRACT OF THE DISCLOSURE Anelectrical resistor which is adjustable as to its resistance value comprising a tubular casing having a resistance element mounted therein and rotatable with respect thereto. The resistance element comprises an elongated substrate of an electrical insulating material, an electrical resistance material on the surface of the substrate and extending on a path between the ends of the substrate, and a separate terminal wire of an electrically conductive metal secured to each end of the substrate and electrically connected to the resistance material. The terminal wires of the resistance element extend through and project beyond the opposite ends of the casing. A contact of an electrically conductive metal is mounted in the casing and slidably engages the resistance material of the resistance element. The contact is mounted in the casing so as to move along the resistance material upon rotation of the casing with respect to the resistance element. An electrically conductive means within the casing electrically connects the contact to one of the terminals.

The present invention relates to an adjustable electrical resistor, and, more particularly, to an electrical resistor having an outer physical configuration of a fixed resistor, i.e.,-a central body with lead wires extending from the ends of the body, and which can be adjusted as to its resistance value.

In'the'construction of electronic circuits, it is often desirable to have an electrical resistor of a size and configuration of a standard resistor of fixed resistance value, i.e.,- a central body portion having a terminal wire extending from each end thereof, but which can be adjusted as to its resistance value. Such a resistor should be capable ofbeing adjusted as to its resistance value after it is assembled in theelectronic circuit either by connecting the terminal wires directly to the terminal of other electronic components forming the circuit or by mounting the resistor'on a printed circuit board. Such an adjustable resistor is particularly useful in the designing of new electronic circuits for which the exact resistance value of the resistors required for the circuit cannot be accurately determined until the circuit is completely assembled. By using an adjustable resistor, the exact resistance value required by the circuit can be easily obtained after the circuit is completely assembled. By having an adjustable resistor which is of the same size and configuration of a resistor of fixed resistance value, the space and position of the'fixed value resistor which will be finally used in the circuit can be determined. This is particularly important when the electronic components of the circuit are mounted on a printed circuit board.

It isfan object of the present invention to provide a novel adjustable resistor.

' It is another' object of the present invention to provide an electrical resistor which can be adjusted as to its resistance value after the'resistor is connected in an electronic circuit. C i

' It is'still another object of the present invention to provide an electrical resistor which can be adjusted as to its resistance value and'of a physical configuration of a standard resistor of fixed resistance value.

Patented Oct. 1, 1968 ice:

Other objects will appear hereinafter.

For the purpose of illustrating the invention, there is shown in the drawings forms which are presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown.

FIGURE 1 is a longitudinal sectional view of one form of the adjustable resistor of the present invention.

FIGURE 2 is a sectional view taken along line 2-2 of FIGURE 1.

FIGURE 3 is a longitudinal sectional view of another form of the adjustable resistor of the present invention.

FIGURE 4 is a sectional view taken along line 44 of FIGURE 3.

Referring initially to FIGURES 1 and 2 of the drawing, one form of the adjustable resistor of the present invention is generally designated as 10. In general, adjustable resistor comprises a tubular casing 12, a resistance element 14 within the casing 12, and rotatable with respect to the casing, and a contact member 16 slidably engaging the resistance element 14 and movable along the resistance element upon rotation of the resistance element with respect to the casing.

Resistance element 14 comprises a cylindrical substrate 18 of an electrical insulating material, such as a plastic or ceramic, coated on its outer cylindrical surface with a film 20 of a resistance material. The resistance film 20 may be of any well-known resistance material, such as carbon, a metal, a metal alloy or a mixture of metals either alone or dispersed in a binder, such as a plastic or glass. Termination films 22a and 22b are coated over the end surfaces of the substrate 18 and extend over the end portions of the resistance film 20. The termination films 22a and 22b are of an electrically conductive metal, such as copper, gold or silver. A groove 24 is provided through the resistance film 20 and into the substrate 18. The groove 24 extends helically around the substrate 18 between the termination films 22a and 22b. The groove forms the resistance film 20 as a helical resistance path extending between the termination films 22a and 22b. Terminal wires 26a and 26b of an electrical conductive metal are secured to the end surface of the substrate 18 and extend longitudinally therefrom. The terminal wires 26a and 26b have heads 28a and 28b respectively on their ends which abut against the termination films 22a and 22b respectively. The terminal wires 26a and 2611 are mechanically secured to the substrate 18 and electrically connected to the termination films 22a and 22b by films 3030 of solder or a suitable electrically conductive cement, I

Casing 12 is of an electrical insulating material, such as a plastic or ceramic, and has radially inwardly extending flanges 32a and 32b at its ends. As shown in FIGURE 2, casing 12 is formed from two mating, semicylindrical sections 12:; and 12b. The section 12a has a rib 34 extending longitudinally along one edge thereof which fits into a groove 36 in the mating edge of the other section 12b so as to properly align the two sections. The two sections 12:: and 12b are secured together by a suitable cement. A groove 38 is provided in the cylindrical inner surface of the casing section 120. Groove 38 extends longitudinally along the casing 12 between the flanges 32a and 32b. Although the casing 12 is shown as having a cylindrical outer surface, the casing may be square or rectangular.

Resistance element 14 is mounted in the casing 12 with the terminal wires 26a and 26b extending through the flanges 32a and 32b respectively and projecting beyond the ends of the casing. Annular, metal bushings 40a and 43b are secured to the inner surface of the casing flanges 32a and 32b respectively. The terminal wires 26a and 26b extend through and are rotatably supported by the bushings 40a and 40b respectively. A contact strip 42 of an electrically conductive metal is seated on and extends along the bottom of the casing groove 38. The contact strip 42 has an arm 44 at one end thereof which extends across the open end of the casing 12. The terminal wire 26b extends through and electrically contacts the arm 44 so that the terminal wire 26b is electrically connected to the contact strip 42.

Contact member 14 comprises a C-shaped spring member 46 of an electrically conductive metal which fits around the resistance element substrate 18. Spring member 46 has a radially inwardl extending dimple 48 at one end thereof which slidably engages the resistance film 20 on the substrate 18. A guide lug 50 of an electrically insulating material, such as a plastic or ceramic, is seated in a depression 52 in the other end of the spring member 46 and extends into the helical groove 24 in the substrate 18. A pair of spring arms 54 project from the side edges of the spring member 46 at the other end thereof. The spring arms 54 extend into the groove 38 in the casing 12 and slidably engage the contact strip 42. Thus, the resistance film 20 is electrically connected to the terminal wire 26!; through the contact member 16 and the contact strip 42 as well as through the termination film 22b and solder layer 30.

In the use of the resistor 10, the resistance value of the resistor is adjusted by rotating the resistance element 14 with respect to the casing 12. This can be achieved by either holding the casing 12 stationary and rotating the resistance element 14 by the terminal wires 26a and 26b or by holding the resistance element stationary and rotating the casing. Rotation of the casing 12 with respect to the resistance element 14 also rotates the contact member 16 with respect to the resistance element 14. The contact member 16 is also moved longitudinally with respect to the casing 12 and the resistance element 14 because of the guide lug 50 riding in the helical groove 24 in the resistance element. Thus, the contact member 14 follows the helical path of the groove 24 so that the dimple 48 in the contact spring member 46 follows the helical path of the resistance film 20. Since electrical current will flow through the path of least resistance and the contact member 14 and the contact strip 42 have an electrical resist ance much less than that of the resistance film 20, the resistance value of the resistor as measured between the terminal wires 26a and 26b will be the electrical resistance value of the length of the resistance film between the terminal wire 26a and the dimple 48 of the contact spring member 46. Therefore, by moving the dimple 48 of the contact spring member 46 along the path of the resistance film 20 through rotation of the casing 12 with respect to the resistance element 14, the resistance value of the resistor 10 can be adjusted to any desired value within the range of the maximum resistance value of the resistance film 20.

The resistor 10 of the present invention can be connected into an electrical circuit in the normal manner of so connecting any electrical resistor, i.e., by either connecting the terminal wires 26a and 26b to the terminal wires of other electrical components or by mounting the resistor 10 on a printed circuit board. Since the adjustment of the resistance value of the resistor 10 can be accomplished by rotating the casing 12 and does not cause any movement of the terminal wires 26a and 26b with respect to each other, the adjustment can be done after the resistor 10 is connected in the electrical circuits. If it is desired to maintain the resistance value of the resistor 10 at any adjusted value, this can be accomplished by merely soldering the terminal wires 26a and 26b to the metal bushings 40a and 40b to prevent any further rotation of the casing 12 with respect to the resistance element 14.

Referring to FIGURES 3 and 4, a modification of the adjustable resistor of the present invention is generally designated as 56. Adjustable resistor 56 is similar to the adjustable resistor 10 shown in FIGURES l and 2 in 4 that it comprises a tubular casing 58, a resistance element 60 within the casing 58 and rotatable with respect to the casing, and a contact member 62 slidably engaging the resistance element 60 and movable along the resistance element upon rotation of the resistance element with respect to the casing.

Resistance element 60 comprises a substrate 64 of an electrical insulating material, such as a plastic or ceramic, which is rectangular in transverse cross section. A film 66 of a resistance material is coated on one of the surfaces of the substrate 64 and extends the full length of the substrate. A film 68 of an electrically conductive material is coated on the surface of the substrate 64 opposite to the surface on which the resistance film 66 is coated. As shown in FIGURE 3, the conductive film extends from one end of the substrate 64 to a point spaced from the other end of the substrate. Termination films 70a and 70b of an electrically conductive material are coated over the end surfaces of the substrate 64. Termination film 70a extends over the adjacent end portion of the resistance film 66 so as to be electrically connected thereto, and termination film 70b extends over the adjacent end positions of the resistance film 66 and the conductive film 68 so as to be electrically connected thereto. Terminal wires 72a and 72b of an electrical conductive metal are secured to the end surfaces of the substrate 64 and extend longitudinally therefrom. The terminal wires 72a and 72b have heads 74a and 74b respectively on their ends which abut against the termination films 70a and 70b respectively. The terminal wires 72a and 72b are mechanically secured to the substrate 64 and electrically connected to the termination films 70a and 70b by a layer of solder or a suitable electrically conductive cement. Thus, the terminal wire 72a is electrically connected to one end of the resistance film 66 through the termination film 70a and the terminal wire 72b is electrically connected to the other end of the resistance film 66 as well as to the conductive film 68 through the termination film 70b.

Casing 58 is similar in construction to the casing 12 of the resistor 10 shown in FIGURE 1 in that it is of an electrical insulating material, such as a plastic or ceramic, and has radially inwardly extending flanges 76a and 76b at its ends. Also, as shown in FIGURE 4, casing 58 is formed from two mating semi-cylindrical sections 58a and 58b. The section 58a has a rib 78 extending longitudinally along one edge thereof which fits into a groove 80 in the mating edge of the other section 58]) so as to properly align the two sections. The two sections 58a and 58b are secured together by a suitable cement. A groove 82 is provided in the inner cylindrical surface of the casing 58 and extends helically around and along the inner I surface of the casing.

Resistance element 60 is mounted in the casing 58 with the terminal wires 72a and 72b extending through the flanges 76a and 76b respectively and projecting beyond the ends of the casing. Annular metal bushings 84a and 84b are secured to the inner surface of the casing flanges 76a and 76b respectively. The terminal wires 72a and 72b extend through and are rotatably supported by the bushings 84a and 84b respectively.

Contact member 62 comprises an annular contact carrier 86 of an electrical insulating material, such as a plastic, within the casing 58 and encircling the resistance element substrate 64. As shown in FIGURE 4, the contact carrier 86 has a substantially D-shaped central opening therethrough providing the contact carrier with an internal fiat surface 88 which slidably engages a noncoated surface of the resistance element substrate 64. The engagement of the contact carrier flat surface 88 with the substrate 64 prevents relative rotation between the contact carrier 86 and the resistance element 64 but permits relative longitudinal movement therebetween. The contact carrier 86 has a radially outward extending guide rib 90 on its outer surface which extends in a helical path of. a pitch corresponding to the pitch of: the helical groove 82 in the casing 58. The guide rib 90 extends into the helical groove 82. A C-shaped contact spring 92 of an electrically conductive metal is secured to the arcuate portion of the inner surface of the contact carrier 86. The contact spring 92 has a lip 94 at one end which slidably engages the resistance film 66 and a contact lip 96 at its other end which slidably engages the conductive film 68. Thus, the resistance film 66 is electrically connected to the terminal wire 72b through the contact spring 92 and the conductive film 68, as well as directly through the termination film 7012.

In the use of the resistor 56, the resistance value of the resistor is adjusted by rotating the resistance element 60 with regard to the casing 58 in the same manner as described with regard to the resistor shown in FIG- URES 1 and 2. Rotation of the casing 58 with respect to the resistance element 60 also rotates the contact member 62 with respect to the casing. The contact member 62 is also moved longitudinally with respect to the resistance element 64 because of the guide rib 90 riding in the helical groove 82 in the casing. Thus, the contact lips 94 and 96 of the contact spring 92 slide longitudinally along the resistance film 66 and the conductive film 68 respectively. Since the contact spring 92 and the conductive film 68 are of a lower electrical resistance than the resistance film 66, the resistance value of the resistor 56 as measured between the terminal wires 72a and 72b Will be the electrical resistance value of the length of the resistance film '66 between the terminal wire 72a and the contact lip 94 of the contact spring 92. Therefore, by moving the contact spring 92 along the resistance film 66 through rotation of the casing 58 with respect to the resistance element 64, the resistance value of the resistor 56 can be adjusted to any desired value within the range of the maximum resistance value of the resistance film 66. The resistor 56 of the present invention can be used in the same manner previously described with regard to the resistor 10 of FIGURES 1 and 2.

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification as indicating the scope of the invention.

I claim:

1. An adjustable electrical resistor comprising a tubular casing of an electrical insulating material; an electrical resistance element within the casing and rotatable with respect to the casing, said resistance element comprising an elongated substrate of an electrical insulating ma-, terial, an electrical resistance material on the surface of the substrate and extending in a path between the ends of the substrate, and a separate terminal Wire of an electrically conductive metal secured to each end of the substrate and electrically connected to the resistance material, said terminal wires extending through and projecting from the ends of the casing; a contact of an electrically conductive material within the casing and slidably engaging the resistance material; means for moving the contact along the path of the resistance material upon relative rotation of the casing with respect to the resistance element; and electrically conductive means within the casing and electrically connecting the contact to one of the terminal Wires.

2. An adjustable electrical resistor in accordance with claim 1 in which the resistance element substrate is cylindrical, the resistance material extends in a helical path around and along the substrate, the substrate has a groove in its surface extending in a helical path between the turns of the resistance material path, a guide lug of an electrical insulating material carried by the contact and slidably fitting into the groove in the substrate so that the contact follows the helical path of the resistance material upon relative rotation of the contact and the resistance element, and means between the contact and the casing preventing relative rotation between the contact and the casing but permitting the contact to move longitudinally with respect to the casing.

3. An adjustable electrical resistor in accordance with claim 2 in which the the means preventing relative rotation between the contact and the casing comprises a groove in the inner surface of the casing extending longitudinally along the casing and an arm on said contact slidably fitting into said groove in the casing.

4. An adjustable electrical resistor in accordance with claim 3 in which the means electrically connecting the contact to the one terminal wire comprises a strip of electrically conductive material within and extending along the groove in the casing, said strip being electrically connected at one end to said one terminal wire and the arm on said contact is of an electrically conductive material and slidably engages said strip.

5. An adjustable electrical resistor in accordance with claim 1 in which the resistance element substrate is rectangular in transverse cross-section, the resistance material extends along one flat surface of said substrate, the casing has a groove in its inner surface extending helically around and along said inner surface, guide means carried by the contact and slidably extending into the helical groove in the casing and means preventing relative rotation between the contact and the resistance element but permitting the contact to move longitudinally with respect to the resistance element.

6. An adjustable electrical resistor in accordance with claim 5 in which the guide means comprising an annular contact carrier surrounding the contact and the resistance element, a guide rib projecting from the outer surface of the contact carrier and slidably fitting into the helical groove in the casing, and the means preventing relative rotation of the contact with respect to the resistance element comprises a flat surface on the interior of said contact carrier slidably engaging a flat surface of the substrate.

7. An adjustable electrical resistor in accordance with claim -6 in which the means electrically connecting the contact to the one terminal wire comprises an electrically conductive material on and extending along a fiat surface of the substrate, said electrically conductive material being electrically connected to said one terminal and said contact slidably engaging said electrically conductive material.

References Cited UNITED STATES PATENTS 1,535,898 4/1925 Camp 338-183 1,832,466 11/1931 Means 338143 2,632,076 3/1953 Clements 338183 X 2,938,396 5/1960 Nicolosi et a1. 338-143 X 3,085,217 4/1963 Bourns et a1 338-176 X ROBERT K. SCHAEFER, Primary Examiner.

H. I-IOHAUSER, Assistant Examiner.

U.S. DEPARTMENT OF COMMERCE PATENT OFFICE Washington, DC. 20231 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent' No. 3 ,404, 361 October 1, 1968 George W Wood It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

In'the headin'g'to the printed specificationyline 5, "IRC, Inc. Philadelplria, Par" should read"''-*- TRW"'Ir"1c., a corporation of Ohio Signed and "sealed this 3rd" day of March 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR

Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer 

